I. Field of the Invention
This invention relates generally to vehicle mounted roof racks for transporting loads, and more particularly to a movable ladder rack that can be used to readily raise and lower a ladder onto and from the roof of a motor vehicle, such as a truck or van.
II. Discussion of the Prior Art
In my earlier U.S. Pat. Nos. 5,297,912, 6,092,972, 6,099,231 and in my currently pending application Ser. No. 09/758,729, filed Jan. 11, 2001, the teachings of which are hereby incorporated by reference, there are described different designs of truck or van-mounted ladder racks that facilitate the loading and unloading of one or more ladders with respect to the vehicle""s roof. These devices comprise front and rear four-bar linkage assemblies that include a stationary member which is adapted to rigidly affixed to the vehicle""s roof or to cross-members that clamp to the vehicle""s roof, and a ladder support member pivotally joined to the stationary member by a pair of transversely spaced links. A drive shaft is journaled for rotation in the stationary members of the front and rear four-bar linkage assemblies and is rigidly affixed to one of the pair of links of the front and rear four-bar linkage assemblies. Thus, when the drive shaft is rotated, either manually with a crank or automatically by means of a motor, ladders resting on the front and rear ladder support members are lifted and rotated from a position parallel to the vehicle""s roof to a position parallel to the vehicle""s side during an unloading maneuver. When reloading ladders onto the vehicle, the drive shaft is rotated in an opposite direction to raise and rotate the ladder load onto the vehicle""s roof.
In my earlier designs described in the aforereferenced patents, the four-bar linkages have been designed such that the top and foot of the ladders remain generally horizontal throughout their range of motion as the drive shaft is rotated. This design featured significant lowering of the ladder""s center of gravity, thus requiring still significant forces.
While the earlier designs reflected in the above-listed patents greatly simplify the loading and unloading of heavy extension ladders onto and from transport vehicles, it is deemed advantageous to provide a rotatable ladder rack assembly for a motor vehicle that requires less force to be applied during the unloading and reloading operations.
In accordance with the present invention, I have redesigned the frontmost four-bar linkage assembly so that as a ladder load is transferred from the vehicle""s roof to its position alongside the vehicle, the front or top end of the ladder is at an increased elevation relative to its foot such that the ladder is inclined relative to the horizontal. The height drop from a roof top position to the lowered disposition is reduced and, therefore, requires less force to operate. With the inclined position, the ladder feet are lowered further and the user is then better able to grasp the ladder at its foot end while the top or front end thereof is still engaged and supported by the front ladder support member. The foot of the ladder can be lifted free of the rear ladder support member and lowered to the ground. Because the top end of the ladder is still being supported by the front ladder support member, less force is required to accomplish the maneuver.
The user may then move to a location along the side of the vehicle to the approximate center of mass of the ladder, whereupon the front portion of the ladder is lifted to disengage it from the front ladder support member and the ladder can be carried to the worksite.